It may be desirable to use a metal gate electrode when making a MOS field-effect transistor that includes a high-k gate dielectric. When forming such a metal gate electrode, it may be necessary to remove portions of a previously deposited very thin metal layer. As shown in FIG. 1a, patterned masking layer 102 may define sections of metal layer 101 to be removed. If a wet etch process is applied to remove part of metal layer 101, that process may etch metal layer 101 isotropically. As a consequence, part of metal layer 101 may be etched from beneath masking layer 102, as FIG. 1b illustrates. The resulting undercut may have adverse consequences.
Accordingly, there is a need for an improved process for etching a very thin metal layer. There is a need for such a process that may enable part of such a layer to be removed, without removing significant portions of it from beneath an overlying masking layer. The method of the present invention provides such a process.
Features shown in these figures are not intended to be drawn to scale.